The preferable electrode catalyst for use in the direct methanol fuel cell (DMFC) is the ones made of platinum or platinum alloy. There is a suitable method for preparing catalysts made of platinum or platinum alloy, which is the colloidal stabilization method. This method involves the implementation of a reduction reaction of a platinum precursor or a platinum alloy precursor with a reducing agent, which is carried out in a solvent and in the presence of a stabilizer, in order to form a suspension containing colloidal particles of platinum or platinum alloy. Because the stabilizer cannot be removed easily, the colloidal platinum or platinum alloy catalyst as obtained is generally used for catalysis directly, or is used to deposit on a carrier then subject the carrier to temperature higher than 200° C. to remove the stabilizer, prior to its use in catalysis. However, the presence of the stabilizer, or the removal of the stabilizer at temperature higher than 200° C., both have adverse effects on the use of platinum or platinum alloy catalyst as DMFC electrode catalyst.
In U.S. Patent 2004/0087441A1, a colloidal stabilization method for preparing platinum or platinum alloy catalyst is disclosed, wherein ethylene glycol is used as the solvent, the reducing agent, and the stabilizer at the same time. Since this method uses only ethylene glycol, it is possible to use the electrochemical oxidation method and/or heating to a temperature less than 200° C. in air to remove the products generated from reduction reaction from the platinum or platinum alloy catalyst. As a result, the adverse effects on platinum or platinum alloy catalyst mentioned in the previous paragraph can be prevented. In this method, the resultant particle size of the platinum or platinum alloy catalyst (between 0.8 to 10 nm) can be adjusted by altering the concentration of NaOH in the reaction compounds. The method can further comprise a step in which a carrier is added to the reaction mixture before reduction reaction is carried out, so that platinum or platinum alloy catalyst can be deposited on a carrier. The method can also further comprise another step in which a carrier is immersed in a suspension resulting from reduction reaction, or coated with particles of platinum or platinum alloy catalyst, so that carriers that has been coated with platinum or platinum alloy catalyst can be obtained. The disclosures of U.S. Patent 2004/0087441A1 is incorporated herein by reference.
Although U.S. Patent 2004/0087441A1 has improved the method for preparing platinum or platinum alloy catalyst, the method of electrochemical oxidation and/or heating to temperature less than 200° C. in air to remove the products generated from reduction reaction from the platinum or platinum alloy catalyst is still less than ideal, and can only be used when ethylene glycol is used as the solvent, the reducing agent, and stabilizer at the same time.